1. Field of the Invention
The present invention relates to a packet repeater machine and packet relay method for inter-connecting networks. The present invention is applied, for example, to a gateway machine for relaying a local network and global network.
2. Description of Related Art
A technology to construct a global communication network by connecting such a local network as a corporate LAN (Local Area Network) to such a global network as the Internet has been known.
In a global network, a global network address to uniquely identify a local machine in the world, that is, a global address, is assigned to an individual local machine. A known global address is, for example, the IP (Internet Protocol) address. Local machines include a server machine. So by using the global address, a server machine in a local network can be uniquely identified. In a global network, a communication destination is specified by the global address for transmitting/receiving data packets.
In a local network, on the other hand, an address unique to the local network, that is, a local address, may be used. The local address is used to identify a terminal or a server machine within the local network. A known local address standard is, for example, the one specified in RFC 1597 for TCP/IP (Transmission Control Protocol/Internet Protocol). In this standard, only a special address in a range called the xe2x80x9cprivate address spacexe2x80x9d is used. A local address cannot be used in a global network. Therefore, a machine directly connected to a global network or a machine connected to another local network cannot identify a machine in the local network by the local address.
When a machine outside a local network communicates with a machine in the local network, relay processing involving the conversion of addresses is executed. This relay processing is executed, for example, by a gateway machine.
A gateway machine has the function to execute mutual conversion between a global address and a local address. This function is called NAT (Network Address Translation), and was standardized by RFC 1631 for TCP/IP. By using the NAT function, communication between a machine outside a local network and a machine inside the local network becomes possible.
When a local network is connected to a global network, a server machine in the local network becomes to be randomly accessed by an unspecified number of general public users worldwide, anytime, day or night. Therefore, it is desirable for the server machine to accept access all the time non-stop. For a server machine to function as a Web server or FTP (File Transfer Protocol) server, in particular, accepting real-time random access is required.
To meet such a requirement, a plurality of server machines having the same function may be installed in one local network. In this case, access from the global network can always be accepted since one of the server machines can be run, even while a server machine is shutdown for maintenance, inspection, updating or changing service content, or for upgrading to a higher function machine. Generally a machine which is operating is called an xe2x80x9cactive system server machinexe2x80x9d, and a machine which is not operating is called a xe2x80x9cstandby system server machinexe2x80x9d. When an active system server machine stops operation and becomes a standby system server machine for maintenance, inspection or other reason, a standby system server machine begins operation and becomes an active system server machine. This operation is referred to as xe2x80x9cswitching of systemsxe2x80x9d.
To execute switching of systems, the active system server machine receives the data packets sent to the standby server machine. Conventionally, data packets addressed to the standby system server machine have been received by the active system server machine by rewriting the registration content of the DNS (Domain Name System) server each time a switching of systems is executed. The DNS server is a name server to convert the host name of a machine to be accessed to such a network address as the IP address. Details on DNS are specified in RFC 1034 for the TCP/IP standard. By rewriting the network address of a server machine, which will be switched to a standby system, to the network address of a server machine, which will be switched to an active system, data packets are always received by the server machine running at that time, that is, by the active system server machine. Therefore another machine which accesses the server machine via a global network does not have to recognize the switching of systems.
However, the method of rewriting the network address of the DNS server can be used when the server machine to be accessed is specified by the host name, but cannot be used when the server machine to be accessed is specified by the network address from the beginning. The host name is used more frequently than the network address as the server specification method in WWW (World Wide Web) browsers since the method of using the host name is more user friendly and is ergonomically better. This is because a character string, which is easy to remember, can be used for the host name, while a network address is expressed with a numeric string, which has no meaning. However, a method of using the network address is also used as the server specification method in WWW browsers. Therefore it is desirable for the active system server machine to receive the data packets sent to the network address of the standby system server machine.
Also, the method of rewriting the network address of the DNS server cannot be used for a local network which does not have a DNS server. For example, in the case of a small scale LAN limited to a small number of information processing units, such as SOHOMO (Small Office Home Office Mobile Office), a DNS server is often not installed in the network. Generally, a small LAN uses a DNS server outside the network when a DNS server is necessary, so as to decrease the cost required for installation and operation of the server. A DNS server outside the network can be accessed by, for example, joining the DNS server access service of the ISP (Internet Service Provider). In the case of a local network, where a DNS server is not installed or a local network which uses a DNS server outside the network, a method of rewriting the network address of a DNS server cannot be used.
It is an object of the present invention to provide a technology which can switch the address of a machine, even when the machine is specified by a network address, and can switch the address of a machine without using a DNS server.
A packet repeater machine in accordance with the present invention comprises: forward information storage means for storing the relationship between a forward origination address and a forward destination address; forward registration means for registering the forward origination address and the forward destination address to the forward information storage means based on input information from the outside; and header conversion means for converting a destination address to the forward destination address when the destination address, which is stored in a packet to be transmitted from a first network to a second network, matches the forward origination address registered in the forward information storage means.
By rewriting the destination address with the forward destination address using the packet repeater machine, an address can be converted using a simple configuration.
A packet relay method in accordance with the present invention comprises steps of: registering the forward origination address and the forward destination address in the forward information storage means based on input information from outside; and executing header conversion processing for converting a destination address to the forward destination address when the destination address, which is stored in a packet to be transmitted from the first network to the second network, matches with the forward origination address registered in the forward information storage means.
By executing processing, rewriting the destination address with the forward destination address as a part of packet relay processing, an address can easily be converted.